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From: "M. Strobel" <sorry_no_mail_here@nowhere.dee>
Newsgroups: comp.lang.php
Subject: Re: Fast/Easy way to extract a column from multi-dimensional array?
Date: Fri, 27 Jan 2012 22:49:29 +0100
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Am 27.01.2012 21:50, schrieb J.O. Aho:
> John Drako wrote:
>> I'm looking for a way to get all the values from the column of a two
>> dimensional array.
>>
>> For example, I have a query on a mysql database that returns 10 rows
>> from the database, I would like to quickly (read low cpu load) extract
>> all the IDs from all the rows returned to reuse in another query.
>>
>> So let's say I use:
>>
>> $arr = mysqli_fetch_all($result, MYSQLI_ASSOC);
>>
>> and $arr looks like:
>>
>> RecordID, name, last name, title
>> RecordID, name, last name, title
>> RecordID, name, last name, title
>> RecordID, name, last name, title
>> RecordID, name, last name, title
>> RecordID, name, last name, title
>> etc...
>>
>> I need to get all the 'RecordID' from the results to reuse in other
>> queries.
>>
>> Is there a built in PHP function (compiled code) to accomplish this?
>> I've read the definitions of all the functions related to arrays and if
>> it exists, I didn't find it.
> 
> There is no function which will do it, but there are ways to make it quite simple
> 
> <?php
> 
> // Assume we got the values out of the database
> $arr = array(
>         array('RecordID' => 1, 'name' =>'A'),
>         array('RecordID' => 2, 'name' =>'B'),
>         array('RecordID' => 3, 'name' =>'C'),
>         array('RecordID' => 4, 'name' =>'D'),
>         array('RecordID' => 5, 'name' =>'E')
> );
> 

Yes, you get an array of arrays.

> // this is a function which will only get the RecordID
> function getRecordID($item, $key, $newarray) {
>         if($key == 'RecordID')
>                 $newarray[]= $item;
> }
> 
> // This is the array where to store the IDs
> $arr_of_id = array();
> 
> // here we do fetch all the IDs
> array_walk_recursive($arr, 'getRecordID',&$arr_of_id);
> 
> // Here you see we got them all
> var_dump($arr_of_id);
> ?>
> 
> 
>> The site is very busy and CPU cycles count. I'm trying to avoid left
>> joining three gigantic tables.
> 
> I think you will need less CPU with the left join, I suggest you look at "having" if
> you want to use a smaller range in the joins.
> 
> Don't forget, if you have something you fetch often and which seldom changes, it can
> be wise to cache those somewhere (either use MySQLs built in cache or memcached or
> similar).
> 

Yes, databases are made for joining. Think twice before doing it in your script.

I am answering to your post because you write exactly what I thought when reading the
question.

/Str.